To Create a Signature Cell Using a Model

From the ribbon, select File > New.
The New dialog opens.
Enter a new file name in the Files field and press OK.
The new DGN opens.
From the ribbon Drawing workflow, select Home > Primary > Models.
The Models dialog opens.
From the Models dialog, select the Create a Model tool.
The Create Model dialog opens.
Do one of the following:

Select Design or Sheet in the Type field.

or
Select Design from Seed or Sheet from Seed in the Type field.
Do one of the following:

If Design or Sheet was selected, choose a 2D seed file. You can create a 3D signature but 2D is recommended.

or
If Design from Seed or Sheet from Seed was selected, use the Change Seed Mode icon to browse for the desired seed file.
Enter Signature in the Name field.
Turn on the Can be placed as a cell check box.
Turn off the Create A View Group check box.
Select Point in the Cell Type field.
Click OK.
A new model is created.
From the ribbon Drawing workflow, select Utilities > Security > Sign.
The Digital Signatures dialog opens.
From the Digital Signatures dialog, select the Add Hidden Digital Model Signature icon.
The Add Hidden Digital Model Signature dialog opens.
Select a certificate installed on your machine with the Browse icon and then click OK.
Verify that the model has been signed by a green check mark in the Verified column on the Digital Signatures dialog.